Nebulizers, or atomizers as they are sometimes called, are devices that generate a fine spray or aerosol from a liquid. A particularly useful application for nebulizers is to provide a fine spray containing a dissolved or a suspended particulate drug for administration to a patient by inhalation.
Piezo-mesh based nebulizers are commonly used to generate aerosols in such drug delivery apparatus, whereby for instance a piezoelectric element vibrates a nozzle plate (otherwise referred to as a mesh) to produce the fine aerosol spray. Typically, the holes in the nozzle plate have a diameter of around 2.5 μm and there can be of the order of 5000 nozzles in a typical nozzle plate.
In some nebulizers the piezoelectric element is bonded to a nozzle plate element, whereas in other nebulizers the nozzle plate element is separate from (i.e. not in contact with) the piezoelectric element (sometimes referred to as piezo-cavity-mesh based nebulizers). An advantage of having the nozzle plate element separate from the piezoelectric element is that the nozzle plate element can be removed from the nebulizer and cleaned or entirely replaced after a certain amount of use. These types of nebulizers are also referred to as flat-plate technology (FPT) aerosol generators.
In the conventional nebulizers, liquid to be nebulized is held in a cavity that includes the piezoelectric element and the mesh, which are spaced a small distance apart (for example 1 mm), and the piezoelectric element is continuously vibrated up and down at high frequency so that liquid that is sitting on top of the piezoelectric element is compressed into and through the mesh to form an atomized (nebulized) plume. The driving signal for the piezoelectric element in the conventional nebulizer is typically a sine wave.
As the dosage regime for a particular medicine may need to be precisely controlled, it is necessary to precisely control (or at least know) the output rate of the nebulized liquid so that the correct amount of medication is administered to the user of the nebulizer.